The purification of immunoglobulins, particularly those of the rat, by classical methods is difficult and laborious. High performance liquid chromatography (HPLC) is a rapid technique capable of high resolution. Secretory IgA has been purified from defatted and decaseinated colostrum and IgM from the euglobulin fraction of serum in a single step. The proteins appear homogenous by immunoelectrophoretic analysis.